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J. R. MCFARLIN.

MEANS FOR DIMMING ELECTRIC HEADLIGHTS.

APPLICATION FILED OCT. 26.1916.

Patented Nov. 25, 1919.

UNITED STATES PATENT OFFICE.

J OHN ROBERT MCFARLIN, F PHILADELPHIA, PENNSYLVANIA, ASSIGNOR T0 ELECTRIC SERVICE SUPPLIES COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORA- TION OF PENNSYLVANIA.

MEANS FOR DIMMING ELECTRIC HEADLIGI-ITS.

Application filed October 26, 1916.

To all whom it may concern:

Be it known that I, JOHN It. MOFARLIN,

i a citizen of the United States, residing in the city of Philadelphia, county of Philadelphia, and State of Pennsylvania, have invented certain Means for Dimming Electric Headlights, of which the following is a specification.

The dimming of high candle power electric head-lights, which is rendered necessary at times, has heretofore been efiected by introducing series resistance into the circuit to effect the absorption of voltage which would otherwise be absorbed by the headlight lamp, and by the use of resistance arranged in shunt relation to the headlight lamp with resulting parallel paths for'the divided current.

The use of series resistance for the absorption of suflicient current to elfect the desired dimming of the lamp is objectionable because it results in dimming the car or other lamps as well as the headlight, and the use of parallel headlight and resistance circuits for dividing the current is objectionable because it decreases the total resistance of the entire lamp circuit and causes the car or other lamps to burn with increased brilliance, with resulting diminution of their lives.

The primary object of the present invention is to provide simple and eflicient means for dimming lights without the foregoing objectionable results due to the absorption of current by series resistance which dims the other lights and to the reduction of total resistance which increases the brilliancy of other lamps.

In my invention, in its preferred form, proportioned series and shunt resistances are combined with the head-light lamp so that the desireddimming is effected without altering the voltage through the other lamps.

My primary object is accomplished conveniently by a circuit from the trolley wire to ground through the car lamps and the head-light lamp for the normal use of the headlight, and, by passing the current from the car lamps through circuits containing properly proportioned resistances in series and shunt relation to the head-light for dimming the same without aflecting the car lamps.

Specification of Letters Patent.

Patented Nov. 25, 1919.

Serial No. 127,797.

2 is a developed diagrammatic view of the circuits; and Fig. 3 is a diagrammatic view illustrating a modification of the layout shown in Fig. 2.

In the application of the invention illustrated in the drawings, the trolley wire 1 is connected by the movable contacting conductor 2 with the lamps 3, in the interior of the car 1, in the parallel conductors 5.

As illustrated in Fig. 2, the parallel conductors 5, containing the car lamps 3, are connected by a conductor 6 containing a switch 7 with the point 8 of a switch 8. The point 8 is connected with a conductor 9 containing the resistance 10, which is connected with the conductor 11 containing the lamp 12 and going to ground, and with the parallel conductor 13 containing the resistance 1 1 and going to the switch point 8 The switch 8 is provided with the further point 8 connected by the conductor 15' with the conductor 11 between the resistance 10 and the lamp 12, with the further. point 8 connected by the conductor 16 with the conductor 11 between the headlight 12 and the ground, and with the switch lever 8 adapted for connecting the point 8 with the point 8 and the point 8 with the point 8.

When the switch 7 is closed and the switch lever 8 connects the points 8 and 8, current flows from the trolley wire 1 through the conductors 2, 5, 6, 7, 8*, 8 8, 15, and 11 to ground, fully lighting the car lamps 3 and the headlight 12, since the resistances 10 and 1 1 are out of circuit. The switch 7 being closed and the switch lever 8 having been shifted to connect the points 8 and 8 the current carried by the conductor 6 is delivered to the conductor 9 and passes through the series resistance 10, whereupon it is divided, part passing through the conductor 11 containing the headlight lamp 12 to ground and the remainder passing through the conductor 13 containing the resistance 14, the switch lever 8 and the conductors 16 and 11 to ground.

As illustrated in Fig. 3, in the normal operation, current passes from the trolley wire 1, through the traveling conductor 2, car lamps 3 in the parallel conductors 5, switch 8, conductor 9, and conductor 11', containing the headlight 12, to ground. When it is desired to dim the headlight, the switch 8 is operated to break the circuit through the conductor 9 and close the circuit containing the resistance 10' connected with the ground conductor 11' containing the headlight 12 in series with the resistance and the circuit comprising the conductor 13' containing the resistance 14' in shunt relation to the resistance 10 and the headlight 12'.

Having described my invention, I claim:

1. In a lighting system, a circuit comprising translating means, a lamp, and means for varying the brillianc of the lamp without varying the current t rough the translating means, comprisin a two position switch and two resistors, sai switch in one position being arranged to shunt one of said resistors and open circuit the other resistor, connecting said lamp directly to said translating means, and in theother position connecti one of said resistors in series between said lamp and translating means and connecting the other resistor in shunt to said lamp.

2. In a lighting system, a circuit comprising translating means, a lamp, and means for varying the brillianc of the lamp without varying the current t rough the translating means, comprising a switch and resistor said switch in one position being arranged to connect said lamp directly to said translating means independently of said resistors and in another position to connect one of said resistors in shunt to said lamp, the other of said resistors then being in series with said lam and translatin means.

In testimony whereof have hereunto set my name this th day of October, 1916.

JOHN ROBERT MGFARLIN. 

